Recently, as the integration degree and the precision of semiconductor devices increase, the formation of ultra-fine photoresist patterns, which have a half pitch of less than 90 nm, is needed in the photolithography process for producing the semiconductor devices. Consequently, the wavelength of an exposure light is reduced to less than 193 nm in the photolithography process, and various technologies for optimizing the pattern forming process have been being developed. In order to form the fine photoresist patterns, it is also necessary to develop photosensitive materials having a low LER(Line Edge Roughness), a law PEB(Post Exposure Baking) temperature sensitivity, and a good dry etching resistance.
In order to improve the resolution and the process margin in the process for forming the photoresist pattern, and to produce a more fine photoresist pattern, the photosensitive photoresist polymer should have a low activation energy in the deprotection reaction of the protecting group, in which the protecting group is adhered to the chain of the photoresist polymer for inhibiting the dissolution of the polymer against a basic solution. For example, the photoresist polymer which can be used for ArF exposure light source include polyacrylate, cycloolefin-maleic anhydride copolymer, polynorbornene and so on, and they are classified into (i) a polymer having the high activation energy protecting group, such as a tertiary butyl group, (ii) a polymer having the medium activation energy protecting group, such as methyl adamantly group or an ethyl adamantly group, and (iii) a polymer having the low activation energy protecting group, such as an acetal group or ketal nobornene group, according to the magnitude of the activation energy of the deprotection reaction of the protecting group which is adhered to the chain of the polymer.
As the photoresist polymer for ArF exposure light source, poly(meth)acrylate having acetal groups, which belong to the low activation energy protecting group, is disclosed in U.S. Pat. No. 4,975,519, U.S. Patent Publication No. 2002-0143130(2002.10.03), and so on. However, it is not disclosed a monomer which have at least 2 (meth)acrylates, particulary, a (meth)acrylate monomer and polymer, which have at least 2 crosslinking alcohol esters as a protecting group for inhibiting the dissolution of the polymer against a basic solution.